1. Field of the Invention
This invention relates to a structure of a photoelectric semiconductor device, and particularly relates to a structure of a light emitted diode and a laser diode that can be fabricated with GaAsP substrate.
2. Description of the Prior Art
The photoelectric semiconductor devices is widely used in various applications, such as the light emitted diode is used to replace the cathode radiation tube recently. The throughput as well as the yield of the light emitted diode is getting more important, and the yield of the light emitted diode is greatly improved. However, the traditional light emitted diode has some problems such as the mismatch between the lattice in the substrate and the light emitting portion of the LED. Furthermore, the oxidation of the widely used material--aluminum may result the problems in manufacturing the traditional LED.
The structure of the traditional LED is shown in FIG. 1, in which the standard structure of the LED includes the window layer 1, the p-cladding layer 2, the active layer 3, the n-cladding layer 4, and the distributed bragged reflector (DBR) layer 5. In the traditional technology, the standard structure of the LED is formed on the substrate made of GaAs. In general, the window layer 1 is made of GaAsP, the p-cladding layer 2 is made of AlGaInP doped with III group semiconductor, the active layer 3 of the multi quantum well (MQW) structure or the double hetero-structure (DH) is made of undoped AlGaInP, the n-cladding layer 4 is made of AlGaInP doped with V group semiconductor, and the DBR layer 5, which is not necessary in a complete LED, is usually made of AlInP and AlGaInP.
Because the lattice constant of the substrate 6 is greater than that of the partial LED structure 10 mentioned above, the lattice mismatch is resulted, and the problems in manufacturing the traditional LED is resulted. The lattice constant of the GaAs substrate 6 is about 5.6 angstroms, so the In ingredient in the partial LED structure 10 must be reduced to 0.482-0.486 to make the lattice match. The structure of the traditional LED is formed by a traditional method described in the following description. As shown in FIG. 1, a distributed bragg reflector (DBR) layer 5 of the first conductivity is formed on the substrate 6. Then form the n-cladding layer 4 on the DBR layer 5, and form the active layer 3 on the n-cladding layer 4 by the LPE (Liquid Phase Expitaxy) method. Subsequently, form a p-cladding layer 2 on the active layer 3 with the additional Zn doping, and then form a window layer 1, which is not necessary for the LED, on the p-cladding layer 2. Finally, form the first electrode 7 on the window layer 1, and form the second electrode 8 on the substrate 6. Thus the traditional LED is manufactured.
In addition, when the phosphorus content z of the active layer 3 (GaAsP,) is equal to 0.39, the manufactured LED mentioned above emits the red light. If the LED is designed to emit the light of short wavelength such as the light of orange color or yellow color, the phosphorus ingredient z of the active layer 3 must be adjusted to 0.75 or 0.85. Furthermore, the adequate material used in fabricating the substrate 6 in the forgoing LED, which emits the light of short wavelength such as the orange or the yellow light, must be changed to GaP. Unfortunately, when the phosphorus content of the active layer 3 is larger than 0.5, the LED can not emit light because of the indirect band gap. In order to overcome the indirect band gap mentioned above, the nitrogen deposition is utilized to result in the isoelectronic center, which overcomes the indirect band gap mentioned above.
If the traditional LED mentioned above is designed to emit the green light, aluminum must be added in manufacturing the traditional LED. Because the aluminum tempts to react with the oxygen, so it is not easy to manufacture the LED emitting the green light according to the traditional method. In addition, the lattice mismatch between the GaAs substrate 6 and the partial LED structure 10 shown in FIG. 1, results in the serious problem in manufacturing the traditional LED mentioned above.